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 * published by the Free Software Foundation.  Oracle designates this

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 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

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package com.sun.jdi.connect.spi;

import java.io.IOException;

/**

 * A connection between a debugger and a target VM which it debugs.

 *

 * <p> A Connection represents a bi-directional communication channel

 * between a debugger and a target VM. A Connection is created when

 * to a Connection by the target VM are read by the debugger in the

 * order in which they were written.

 *

 * <p> A connection is either open or closed. It is open upon creation,

 * and remains open until it is closed. Once closed, it remains closed,

 * and any attempt to invoke an I/O operation upon it will cause a

 * {@link ClosedConnectionException} to be thrown. A connection can

 * be tested by invoking the {@link #isOpen isOpen} method.

 *

 * <p> A Connection is safe for access by multiple concurrent threads,

 * although at most one thread may be reading and at most one thread may

 * be writing at any given time.

 *

 * @since 1.5

 */

public abstract class Connection {

    /**

     * Reads a packet from the target VM.

     *

     * <p> Attempts to read a JDWP packet from the target VM.

     * A read operation may block indefinitely and only returns

     * when it reads all bytes of a packet, or in the case of a

     * transport service that is based on a stream-oriented

     * communication protocol, the end of stream is encountered.

     *

     * <p> Reading a packet does not do any integrity checking on

     * the packet aside from a check that the length of the packet

     * (as indicated by the value of the {@code length} field, the

     * first four bytes of the packet) is 11 or more bytes.

     * If the value of the {@code length} value is less then 11

     * then an {@code IOException} is thrown.

     *

     * <p> Returns a byte array of a length equal to the length

     * of the received packet, or a byte array of length 0 when an

     * end of stream is encountered. If end of stream is encountered

     * after some, but not all bytes of a packet, are read then it

     * is considered an I/O error and an {@code IOException} is

     * thrown. The first byte of the packet is stored in element

     * {@code 0} of the byte array, the second in element {@code 1},

     * and so on. The bytes in the byte array are laid out as per the

     * <a href="{@docRoot}/../specs/jdwp/jdwp-spec.html">

     * JDWP specification</a>. That is, all fields in the packet

     * are in big endian order as per the JDWP specification.

     *

     * <p> This method may be invoked at any time.  If another thread has

     * already initiated a {@link #readPacket readPacket} on this

     * connection then the invocation of this method will block until the

     * first operation is complete.

     *

     * @return  the packet read from the target VM

     *

     * @throws  ClosedConnectionException

     *          If the connection is closed, or another thread closes

     *          the connection while the readPacket is in progress.

     *

     * @throws  java.io.IOException

     *          If the length of the packet (as indictaed by the first

     *          4 bytes) is less than 11 bytes, or an I/O error occurs.

     *

     *

     */

    public abstract byte[] readPacket() throws IOException;

    /**

     * Writes a packet to the target VM.

     *

     * <p> Attempts to write, or send, a JDWP packet to the target VM.

     * A write operation only returns after writing the entire packet

     * to the target VM. Writing the entire packet does not mean

     * the entire packet has been transmitted to the target VM

     * but rather that all bytes have been written to the

     * transport service. A transport service based on a TCP/IP connection

     * may, for example, buffer some or all of the packet before

     * transmission on the network.

     *

     * <p> The byte array provided to this method should be laid out

     * as per the <a

     * href="{@docRoot}/../specs/jdwp/jdwp-spec.html">

     * JDWP specification</a>. That is, all fields in the packet

     * are in big endian order. The first byte, that is element

     * {@code pkt[0]}, is the first byte of the {@code length} field.

     * {@code pkt[1]} is the second byte of the {@code length} field,

     * and so on.

     *

     * <p> Writing a packet does not do any integrity checking on

     * the packet aside from checking the packet length. Checking

     * the packet length requires checking that the value of the

     * {@code length} field (as indicated by the first four bytes

     * of the packet) is 11 or greater. Consequently the length of

     * the byte array provided to this method, that is

     * {@code pkt.length}, must be 11 or more, and must be equal

     * or greater than the value of the {@code length} field. If the

     * length of the byte array is greater than the value of

     * the {@code length} field then all bytes from element

     * {@code pkt[length]} onwards are ignored. In other words,

     * any additional bytes that follow the packet in the byte

     * array are ignored and will not be transmitted to the target

     * VM.

     *

     * <p> A write operation may block or may complete immediately.

     * The exact circumstances when an operation blocks depends on

     * the transport service. In the case of a TCP/IP connection to

     * the target VM, the writePacket method may block if there is

     * network congestion or there is insufficient space to buffer

     * the packet in the underlying network system.

     *

     * <p> This method may be invoked at any time.  If another thread has

     * already initiated a write operation upon this Connection then

     * a subsequent invocation of this method will block until the first

     * operation is complete.

     *

     * @param   pkt

     *          The packet to write to the target VM.

     *

     * @throws  ClosedConnectionException

     *          If the connection is closed, or another thread closes

     *          the connection while the write operation is in progress.

     *

     * @throws  java.io.IOException

     *          If an I/O error occurs.

     *

     * @throws  IllegalArgumentException

     *          If the value of the {@code length} field is invalid,

     *          or the byte array is of insufficient length.

     */

    public abstract void writePacket(byte pkt[]) throws IOException;

    /**

     * Closes this connection.

     *

     * <p> If the connection is already closed then invoking this method

     * has no effect. After a connection is closed, any further attempt

     * calls to {@link #readPacket readPacket} or {@link #writePacket

     * writePacket} will throw a {@link ClosedConnectionException}.

     *

     * <p> Any thread currently blocked in an I/O operation ({@link

     * #readPacket readPacket} or {@link #writePacket writePacket})

     * will throw a {@link ClosedConnectionException}).

     *

     * <p> This method may be invoked at any time.  If some other thread has

     * already invoked it, however, then another invocation will block until

     * the first invocation is complete, after which it will return without

     * effect.

     *

     * @throws  java.io.IOException

     *          If an I/O error occurs

     */

    public abstract void close() throws IOException;

    /**

     * Tells whether or not this connection is open.

     *

     * @return {@code true} if and only if this connection is open

     */

    public abstract boolean isOpen();

}